Next week is the five-year anniversary of the Sandy Hook Elementary School shooting that left 26 dead, including 20 children, in what was formerly the sleepy community of Newtown, Connecticut. Since that shooting, gun-control advocates have clamored, begged and even held sit-ins on the floor of the House of Representatives to get a vote on significant legislation that might bring about greater gun safety in the U.S.

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On Wednesday, advocates finally got a vote on a bill that would close loopholes in the National Criminal Instant Background Check system, or NCIS. But they're incensed that the broadly bipartisan NCIS bill was combined with legislation that forces police officers to recognize concealed carry permits from other states.

The Democrat, who represents Newtown, spent part of Wednesday with the hundreds of family members of gun violence victims who traveled to Washington to mourn and remember their lost loved ones at an annual vigil.

"To take a good bill, to then combine it with something that is unnecessary and reckless, and to do it on the day of the already scheduled 5th national vigil to honor victims of gun violence is beyond offensive," Esty says.

The National Rifle Association has called the Concealed Carry Reciprocity Act its "highest legislative priority," which Esty says was on display when Republican leaders scheduled their gun-rights vote on the same day as the vigil.

"Excruciatingly disrespectful. I'm staggered," Esty says. "That tells you something about who is calling the tune – the piper here is the moneyed interest of the gun lobby. And I'm so disappointed in my colleagues in Congress on the other side of the aisle."

The legislation eventually passed – over loud protests from most Democrats – in a 231-198 vote. Fourteen Republicans opposed it, while six Democrats voted in favor of the bill.

The concealed carry bill allows people to bring their weapons on national park lands and allows police officers who are off-duty to bring guns into highly restrictive school zones.

Critics of the legislation note that it would also allow people to obtain permits in states that will issue them to people convicted of domestic abuse and to use those permits in states that bar the practice.

"I'm very concerned about permit shopping. So if someone can't get a concealed carry permit in Rhode Island, they could go to some nearby state and get a concealed carry permit there, and then all of a sudden it undermines what protections we have in Rhode Island," Democrat Rep. Jim Langevin tells Rolling Stone. "It's a frustrating turn of events when Republicans have improved background checks in one respect, but they're just opening the floodgates to guns being in our community in another respect."

Critics of the concealed carry bill argue it's especially hypocritical for the GOP to be pushing the legislation because it upends states' rights – for instance, by allowing an 18-year-old to get a concealed carry permit in one state and then travel with his gun to a state that has set 21 as the legal age to carry.

"I'm not aware of any law which uses federal power to import the law of one state into another. The last law I can remember that did that was the Fugitive Slave Act of 1852," Rep. Jerry Nadler, now the top Democrat on the House Judiciary Committee, tells Rolling Stone. "Here, in an obnoxious way, it's saying the safety concerns of every state are overridden by the most permissive state."

For their part, supporters of the bill argue the Second Amendment doesn't end at a state's borders, and they deny they were merely carrying water for the NRA.

"No. This is not being driven by the NRA. This is being driven by my farmers and other folks who want to be safe as they travel the country," Republican Rep. Chris Collins tells Rolling Stone.

Collins is from Upstate New York and was one of Donald Trump's leading backers in Congress during the campaign. He says the concealed carry bill is already exciting the GOP base and will increase Trump's popularity.

"This will be so wildly popular and frankly energizing to his base that are now going to see another reason, beyond Neil Gorsuch, why this president is so important to keep this country moving in a direction – constitutional and safety, first and foremost," Collins says.

The vote marks the first Second Amendment vote in this Congress, and both sides of the divide are now preparing to make the issue a central part of next year's midterm elections.

"I think gun safety will be an election issue in 2018," Democratic Sen. Richard Blumenthal of Connecticut tells Rolling Stone. "There's a growing coalition and consensus that America needs to act – that we need to make our communities safer from gun violence. I think we're reaching a tipping point where the barriers are going to break, politically, and it will be in effect on the ballot in 2018."

The NCIS, or background check, piece of the legislation is now in limbo after House leaders combined it with the concealed carry language. A bipartisan group of lawmakers came up with that compromise after the recent shooting at a Texas church left 26 people dead. That gunman should have been barred from purchasing guns because he was convicted of domestic violence abuse while in the Air Force, but military leaders failed to report him to the NCIS database.

While at least two Senate Democrats from states Trump won last November are supportive of some sort of concealed carry bill, the legislation doesn't seem to have enough support to get over the Senate's 60-vote filibuster threshold. That has some Republican senators looking for a way to decouple the bills, which will likely mean taking up the background check bill on its own while leaving the concealed carry debate for another day – or even another Congress.

"I support both bills, but I worry that if you combine them then it's not going to go anywhere so we don't fix the background check system," Texas Sen. John Cornyn, the number-two Republican in the Senate and lead sponsor of the NCIS bill, tells Rolling Stone. "I want to fix the background check system, and I think that's the most urgent thing to do."